DESCRIPTION (Adapted from applicant's description): The purpose of this project is to determine the optimal early and maximal nutrition in extremely low birth weight (ELBW) infants. Currently, it is common practice to limit substrate administration to ELBW neonates in the first days after birth. This results in postnatal malnutrition that causes short-term growth failure that may have consequences for long-term growth and development. We hypothesize that for ELBW infants in the first 24-48 hours of life, an amino acid administration rate comparable to that delivered to the fetus at the same post-conceptional age ("high" intake) is both safe and efficacious in terms of enhanced protein accretion when compared to conventional ("low" intake) amino acid delivery rates, and can avoid the early postnatal malnutrition commonly seen with current nutritional strategies. ELBW infants will be randomized in the first 12 hours of life to 1 versus 3 g/kg/d intravenous amino acids and experimental protein metabolism studies performed after 24-48 hours on parenteral nutrition. Protein balance will be determined by nitrogen balance and stable isotope methodologies. Safety will be assessed by plasma amino acid and blood urea nitrogen concentrations. Glucose and glycerol turnover rate measurements will assess the interactive effects of glucose, fat, and amino acids on protein metabolism. The effect of total non-protein energy intake on protein balance will also be determined. Leucine kinetic studies will be used to determine the mechanisms regulating protein synthesis, breakdown and oxidation in this population at different amino acid intakes. This will be the first randomized study in ELBW neonates immediately after birth that includes an amino acid intake as high as 3 g/kg/d, an intake that approaches the fetal amino acid delivery rate and that theoretically is the desired ELBW infant amino acid intake. If this study demonstrates the safety and efficacy of this amino acid intake, it will set the stage for larger clinical trials on the effect of early, higher amino acid intake on duration of hospitalization, short- and long-term postnatal growth, and neurodevelopmental outcome.